The present invention relates to an inspection unit for a high frequency/high-speed device for ensuring reliable connection between the inspection unit and the device to be inspected, on occasion of inspecting its electrical performance, before a module of a high frequency/high-speed circuit such as an amplifier circuit, a mixer circuit, a filter circuit, a memory, a CPU, etc. or an IC to be incorporated in a mobile phone, for example, has been assembled to a circuit board. In this specification, the term “high frequency” refers to an analogue signal having a high frequency (1 GHz or more), while the term “high-speed” refers to a digital signal having very short pulse width and pulse interval, and both of which are hereinafter collectively referred to as RF (radio frequency).
On occasion of inspecting electrical performance of the RF device such as a semi-conductor wafer, an IC, or a module, insufficient contacts between the terminals may particularly cause fluctuation of impedance or other measurement factors, which may sometimes vary to change measured values. Under the circumstances, such inspection has been conducted by means of a special inspection unit, for example, as shown in FIG. 4A (disclosed in Japanese Patent Publication No. 2001-99889A). In such an inspection, an RF circuit, which is the device to be inspected, is constructed in a form of a module 50 including an amplifier circuit and a mixer circuit, and is housed in a metal casing for avoiding interference with the exterior. The module 50 includes input and output terminals 51, 54 for RF signals, a power supply electrode terminal 52, and a grounding terminal 53, which are provided on a back face of the metal casing. Then, the inspection is conducted by electrically connecting the terminals to respective terminals of a wiring board 66 on which certain wirings for the inspection are arranged.
In the example as shown in FIG. 4A, there are employed contact probes each having a spring and a plunger contained in a metal pipe, one end of the plunger being adapted to be projected to the exterior by the spring and contracted when pushed. The respective electrode terminals are connected by contact probes 63 for RF signals, a contact probe 64 for power supply, and a contact probe 65 for grounding which are contained in a metal block 61 for preventing them from being affected by noises. Each of the contact probes 63 for RF signals is formed in a coaxial structure, using the contact probe as a core conductor and using an inner wall of a through hole in the metal block 61 as an outer conductor, especially for preventing intrusion of noises. In FIG. 4A, denoted with numeral 67 is a coaxial cable, and 68 is a plate for pressing the metal pipes surrounding the contact probes. Such a structure around the contact probes is almost the same in case of an IC socket for inspecting ICs, though such a socket has a different outer shape.
Although FIG. 4A shows only two contact probes 63 for RF signals (for input and output), contact probes 64, 65 each for power supply and for grounding, a large number of these contact probes are actually provided. In the maximum case, the electrode terminals of about 600 pieces per 1 cm2 are provided in a matrix manner with a narrow pitch of about 0.4 mm. Under the circumstances, each of the contact probes has to be extremely small in diameter. Particularly, the contact probe 63 for RF signals has become very small, because it is required to serve as the core conductor of the coaxial structure under certain dimensional relationship with an inner diameter of the through hole which is formed in the metal block 61 as the outer conductor. On the other hand, it is desirable that the contact probe 64 for power supply and the contact probe 65 for grounding are as thick as possible, for the purpose of reducing resistance loss. For this reason, the outer diameters of the contact probes and the inner diameters of the through holes are different depending on the respective contact probes, as shown in FIG. 4B.
Specifically, in a case of constructing an inspection unit in which an interval between the contact probes is 0.5 mm, the contact probes have various values in diameter. For example, the outer diameter d1 of the contact probe 63 for RF signals is 0.2 mm and the inner diameter D1 of the through hole is 0.45 mm, whereas the outer diameter d2 of the contact probe 64 for power supply is 0.3 mm and the inner diameter D2 of the through hole is 0.42 mm, and the outer diameter d3 of the contact probe 65 for grounding is 0.3 mm and the inner diameter D3 of the through hole is 0.4 mm. On the other hand, all the contact probes have the same length L which is set to be 4.0 mm, for example.
As described above, the contact probes and the through holes of the metal block in which the contact probes are disposed have different diameters for usage of respective contact probes, and therefore the conventional inspection unit is constructed in such a manner that the contact probes are disposed in respective positions according to the arrangement of the electrode terminals in a device to be inspected. Meanwhile, such inspection unit is unable to be prepared prior to developing stage, because in the developing stage of the module and IC of this type, various adjustments are continued along with the inspection, and accordingly, there may be changes in the arrangement of the electrode terminals, such as addition of a grounding terminal.
Nevertheless, even in the developing stage, it is impossible to perform accurate inspection unless a reliable inspection unit is employed. Under the circumstances, there is a problem that in a case where various inspection units are prepared in the developing stage, it would lead to an enormous increase of cost. Furthermore, in a case where provisional inspecting tools are used in order to conduct the inspection in the developing stage, and a producer of inspection units starts to produce a definitive version of the inspection unit after completion of the development based on the fixed arrangement of the electrode terminals in the device to be inspected, these may be a problem that it would not be in time for conducting the inspection immediately. Especially in a case where the producer of the inspection unit is different from the developer of the device, the developer of the device generally have a tendency not to disclose the arrangement of the electrode terminals to the producer of the inspection unit to the final stage of the development, in some cases, which is a serious time factor in preparing the inspection unit.